Sustainable Recycling of Spent Li-Ion Batteries and Iron Ore Tailings for Cobalt Ferrite Synthesis and Its Dual Applications as a Photocatalyst in Solar Photo-Fenton Process and an Electrochemical Sensor

This study presents a solution to solid waste problems, focusing on spent lithium-ion batteries (LiBs) and iron ore tailings (IOT) from the Mariana environmental accident in Brazil. The approach involves the production CoFe2O4 from LiBs and IOT, which serves as a catalyst for solar photo-Fenton reactions for methylene blue (MB) decolorization and as an electrochemical sensor for ascorbic acid (AA) detection. Chemical analysis showed recycling potential, with 45.22 ± 0.22% m m−1 Co from LiBs and 14.9 ± 1.5% m m−1 Fe from IOT, determined by inductively coupled plasma atomic emission spectroscopy (ICP OES) and flame atomic absorption spectrometry (FAAS). The sol-gel synthesized CoFe2O4 exhibited a crystallite size of 51.9 ± 1.3 nm and agglomerated crystal clusters. Recycled-CoFe2O4 exhibited a 98.1% MB decolorization efficiency in 60 min under solar irradiation and remained above 92.3% in all 7 reuse cycles. The electrochemical sensor exhibited a coefficient of determination of 0.9987, a sensitivity of 3.352 ± 0.0428 μA mol L−1, and a limit of detection of 0.5511 µM in the concentration range of 1.96 to 23.08 mmol L−1 for AA detection. This study demonstrates the potential of recycled-CoFe2O4 in an environmentally friendly dye removal and as an electrochemical sensor, offering sustainable waste management and resource utilization with solar energy.